This invention relates to the control and electronics art and has particular relationship to the art of controlling the inspection and sorting or classification of articles. A mechanical handling and gauging system to which this invention is applicable is disclosed in Wilks application. This system is conceived for the sorting or classification of fuel pellets for a nuclear reactor. The pellets are inspected in this system for diameter, length, surface flaws and density. The mechanical system includes an array of stations in which each pellet is successively subjected to measurement of one of the parameters. The inspection for diameter and flaws is carried out by sweeping or scanning each pellet lengthwise with a light beam as the pellet rotates. The light beam is shaped to accommodate the measurement. The light beam for diameter measurement is in the form of a vertical ribbon which envelops the pellet transversely producing shadows of elemental transverse slices on a photo-diode array on which the beam, as modified by the pellet, is incident. The light beam for flaw measurement produces a spot on the surface of the pellet lighting elemental areas from which light is reflected to a photo-diode if the surface is unflawed and away from the photo-diode if the surface is flawed. For length inspection a chisel-shaped beam (a flat beam in a horizontal plane) is projected across the length of the pellet as the pellet rotates. Shadows of elemental longitudinal slices of the beam are produced on a photo-diode array on which the beam is incident. To inspect for density, the weight of each pellet is measured and divided by the length. The pellets are moved from station to station by grippers carried by a gripper beam.
The system is capable of carrying out the inspection at a high time rate. Typically 3 pellets per second are inspected for diameter, flaws and length. For weight a pellet is inspected at the rate of 1 every two seconds or more generally 1 every N seconds. In practice all pellets are inspected at the rate of 3 per second for diameter, flaws and length and one pellet in 6 is inspected for mass every two or N seconds. The longer period for weight is required to enable the scale to stop oscillating after it receives the pellet.
In use the pellets are stacked in tubes or cladding of zircaloy or stainless steel to form fuel elements. For effective heating of the coolant and to avoid hot spots it is desirable that the pellet diameter should be maintained within close tolerances so that there is a minimum of annular space between the pellets and the inner wall of the cladding. Typically the diameter of a pellet is 0.1945.+-.0.002 inch. The length is likewise maintained within close tolerances. Typically the length of a pellet is 0.2425.+-.0.020 inch. The weight determines the density and should be maintained within limits to avoid localized heating or cooling. The weight is typically 1 gram.+-.5 milligrams.
It is an object of this invention to provide a control for a mechanical handling and gauging system, typically as disclosed in Wilks application, under whose governance the mechanical system shall operate reliably to inspect fuel pellets at a high time rate and to classify pellets with the dimension criteria within the above-stated close tolerances.
Typically plutonium pellets are inspected. Because of the hazards which plutonium presents, it is desirable that all pellets under inspection be accounted for. It is another object of the invention to provide a control for a mechanical system which shall assure that the above parameters are measured while the pellets move with 100% accountability through the system from a feed hopper to sorting bins i.e., the control must assure that the number of pellets deposited in the bins must equal the number of pellets which enter the array of inspection stations.
It is a further object of the invention to provide a control for a mechanical handling and gauging system for fuel pellets which shall reliably assure, prior to each cycle of inspection, that the system is fully set for inspection and that the pellets to be subject to mesurement and weighing are in their stations properly positioned to be measured or weighed. It is also an object of this invention to provide such a control with facilities for enabling the measurement of the diameter and the length of each pellet precisely.